ANCIENT DNA FROM CHILEAN MUMMIES CONFIRMS EUROPEAN ORIGIN OF SMALLPOX IN...

Researchers from Trinity College Dublin have recovered and analysed the first ancient smallpox virus genomes ever identified in the Americas, according to a study published in the journal Science. The team examined bone samples from two individuals buried in northern Chile between the late 15th and early 17th centuries, finding genetic evidence of smallpox infection in an adult man and woman. Scientists determined that the viral strains belonged to a now-extinct lineage of variola virus positioned evolutionarily between medieval European strains and those circulating in later centuries. The discovery provides direct molecular confirmation that the disease was introduced to the Americas during European colonisation, rather than originating locally.

Before its eradication in 1980, smallpox killed approximately one-third of those infected and caused severe scarring in survivors. Colonial writings and missionary accounts documented its catastrophic impact on Indigenous populations who lacked immunity to the virus. The new genetic analysis shows that the smallpox strains infecting people in the Americas evolved first from European sources, offering what geneticist Shigeki Nakagome of Trinity College Dublin described as clearer understanding of transmission routes through colonisation. The research compared the ancient viral DNA to other known strains, tracing the evolutionary path of the disease across continents and centuries.

The study also revealed that smallpox underwent significant genetic change up to the 16th century, but that its evolution slowed markedly during the height of colonial expansion and major epidemics in the 17th and 18th centuries. According to the researchers, this evolutionary stability may have occurred because the virus reached an optimal form for transmission, aided by the lack of immunity in newly exposed populations. The pace of viral evolution appears to have increased again in the 19th century as vaccination became increasingly widespread and immunity levels rose among populations.